1. Field of the Invention
This invention is a technique for growing amorphous, stoichiometric, native, semiconductor oxide layers with a sharp interface region.
2. Description of the Prior Art
Oxide layers play an important role in semiconductor technology; for example, as insulators in metal oxide semiconductor field effect transistors and as passivating layers and isolating regions in other semiconductor devices.
Techniques for growing oxide layers are well established in the art. In silicon technology two major techniques for the growth of native silicon oxide layers predominate. In the first process a silicon substrate is exposed to oxygen at a temperature of approximately 1100.degree. C. As a result, the silicon and oxygen interact to yield a Si oxide layer. Alternatively, the Si substrate may be exposed to a high energy oxygen plasma which again results in the growth of an oxide layer. Depending upon the energy of the plasma, layers as thick as 5000 angstroms may be fabricated.
While silicon technology is highly developed, comparable technology using compound semiconductors, such as GaAs, has not reached such a degree of sophistication. Such compound semiconductors are highly desirable because of their high band gap and high electron mobility. Consequently, any technique which enables the fabrication of compound semiconductor oxide films is of significant interest. The two techniques mentioned above for oxidizing silicon have been applied to the production of GaAs oxide layers, but both are significantly less practical in such an application. The heating technique is not practical in GaAs because the As is highly volatile at the elevated temperatures required for this technique and the resulting layer is, consequently, not stoichiometric. In addition, at these temperatures the GaAs oxide layer does not remain amorphous but rather crystalizes. The high energy plasma technique on the other hand, results in significant radiation-induced damage and poorly defined interface region between the oxide film and the substrate. Under such circumstances, the interface has associated with it many surface states and trapped charges which make the oxide unsuitable for many device applications.
In an article in the Journal of Applied Physics, Vol. 37, page 2924, 1966, O. A. Weinreich discusses a low temperature plasma oxidation technique for growing GaAs films. The film is grown in a quartz gas discharge tube in which an oxygen plasma is supported. Weinreich indicates that the primary mechanism responsible for the observed film growth involves the extraction of negative oxygen ions from the plasma and their diffusion into the GaAs substrate. Since plasmas have very low negative ion densities, this technique requires plasmas with large charge particle densities and large oxygen background pressures, in order to yield the requisite number of negative oxygen ions. The power necessary to support such plasmas is comparatively high and this has discouraged detailed investigation of this technique. Weinreich's statements regarding the importance of negative oxygen ions suggest that low density plasmas will not be effective, and he and others in the art have avoided for nearly ten years investigation of low density plasmas for this application. This only serves to confirm the persuasiveness of teachings such as Weinreich's to practitioners in the art.